Rotary pump and motor hydraulic transmission



Oct. 19, 1954 J. J. NICOLAS 2,691,868

ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Original Filed Qct. 23, 1946 3 Sheets-Sheet 1 Oct. 19, 1954 J. J.- NICOLAS ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION 3 Sheets-Sheet 2 Original Filed Oct. 23', 1946 Oct. 19, 1954 J. J. NICOLAS 2,691,868

ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Original Filed Oct. 25, 1946 Patented Oct. 19, 1954 ROTARY PUMP AND MOTOR *HYDRAULIC TRANSMISSION Jean Joseph Nicolas, ParisQFrance Original application October 23,1946, Serial No.

705,102, now Patent No. 2,607,298, dated -August 19, 1952.

Divided and this application March 11, 1949, Serial N0. 80,924

Claims priority, application "France November 12, 1945 3 Claims. 1

The present invention relates to a hydraulic transmission comprising a rotary pump and a rotary motor.

The present application is a divisional application of application Serial No. 705,102 filed October 23, 1946, and issued into U. S. Patent No. 2,607,298.

In the above mentioned U. S. Patent No. 2 97,298 a hydraulic apparatus is disclosed which maybe operated 'as a pump or as a motor and which achieves a perfect axial balancing of the rotor by means of the operating fluid. The hydraulic apparatus according to my previous invention also permits a perfect control'of the output of the apparatus.

It is one object of the present invention to make use of the advantageous features of a hydraulic apparatus of this type in an improved highly efficient hydraulic transmission consisting of two hydraulic apparatus of this type.

It is another object of the present invention to provide means in a hydraulic transmission of this type for simultaneously and reversely adjusting the output per revolution of the pump and of the motor constituting the hydraulic transmission.

It is a further object of the present invention to provide a hydraulic transmission in which motor and pump are arranged within a single casing which also envelopes the necessary conduits connecting the pump and the motor.

It is still another object of the present invention to provide a hydraulic transmission in which the motor can be reversed, and in which the transmission ratio can be adjusted during rotation in either direction.

It is also an object of the present invention to provide a hydraulic transmission for motor cars which can be easily operated, and which is provided with operating means for by-passing the rotary pump and for connecting the motor to a hydraulic accumulator to provide hydraulic braking.

With these objects in view the present invention mainly consists in a hydraulic transmission arrangement comprising, in combination, a stationary casing, a driven shaft rotatably mounted in the casing, a motor rotor fixedly secured to the driven shaft and rotatably mounted in the casing, the motor rotor being formed with an inner cavity having a main portion open at one end and bounded by a circular transverse end face, a cylindrical face, and a transverse annular face facing the end face, the motor rotor having an outer surface portion including an 2 annular transverse end face, a cylindrical face, a second tra'nsverse annul'ar "face facing the first annular end face and defining with the inner surface of the casing an annular cavity, a drive shaft rotatably mounted in the casing, a pump rotor mounted on the drive shaft slidable in axial direction and 'nonrotatabl-e, the pump rotor having a stepped cylindrical outer surface fitting into the inner cavity of the motor rotor and closing the main portion, 'the motor rotor having "a cylindrical head portion located in the main portion between the end face and the annu-la'r face and defining with "the pump rotor in the inner "cavity a closed cylindrical pump balancing chamber and an annular pum'p working chamber, stator means, non-rotatably and axially slidably mounted on the inner surface of the casing, and having an annular projecting portion dividing the annular cavity into an annular mot'or balancing chamber and an -an nular motor working chamber, partitioning means secured to the motor rotor "and projecting into the .pump working chamber and into the motor working chamber and dividing each of the working chambers. pump blade means and motor blade means mounted, respectively, on the pump rotor and on the stator means slidable in axial direction, the blade means projecting with one end thereof into the associated balancing chambers and into the associated working chambers and defining in the latter chamber together with the partitioning means suction portions and pressure portions, cammea'ns secured to the partitioning :means and engaging the other end, of the blade means for pushing the same into the associated balancing chambers and out of the working chambers when the blade means :pass the partitioning means durin rotation of the rotor, conduit means in the motor rotor connecting the pressure portion of each Working chamber with the suction portion of the other of the working chambers, first fluid valve means associated'with the pump rotor and being movable between two positions and connecting in one of the positions the pump balancing chamber with the pressure portion of the pump working chamber and in the other position with the suction chamber of the pump working chamber, second fluid valve means associated with the stator means and being movable between twopositions and connecting in one of the positions the motor balancing chamber with the pressure portion of the motor working chamber and in the other position with the suction portion of the motor working chamber,

connecting means connecting the first and second fluid valve means so that each of the fluid valve means moves to the one position thereof when the other of the fluid valve means moves to the other position thereof, whereby the fluid pressure in the balancing chambers is adjusted causing axial movement of the pump rotor and of the stator means for adjusting the volumes of the annular working chambers, and means for adjusting the position of at least one of the fluid valve means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is an axial sectional view of the hydraulic transmission according to the present invention in the position of direct drive taken on line II in Figs. 2 and 12;

Fig. 2 is a cross-sectional view on line IIII in Figs. 1 and 10, the transmission being in an intermediate position;

Fig. 3 is a developed View of cylindrical section taken on line II[III in Fig. 1;

Fig. 4 is a cross-sectional view on line IV-1V of Fig. 3;

Figs. 5 and 6 are fragmentary sectional views illustrating modifications of the means controlling the output;

Figs. 7-9 are fragmentary cross-sectional views illustrating valve positions corresponding to different operational conditions of the hydraulic transmission Fig. 10 is an axial sectional view taken on line XX in Figs. 2 and 12 in a position of the transmission in which the blades are located opposite the partitions and under operational conditions of maximum speed reduction;

Fig. 11 is an isometric view of cam means provided for advancing the blades into the working chambers; and

Fig. 12 is a cross-sectional view taken on line XIIXII of Figs. 1 and 10.

Referring now to the drawings, and more particularly to Figs. 1, 2 and 10, the transmission includes an inner pump rotor 55 mounted on the drive shaft 65 non-rotatable, but slidable in axial direction. The drive shaft 66 is rotatably mounted in a stationary casing 61 which also rotatably supports the driven shaft 63 which is fixedly secured to the motor rotor 52. The motor rotor 62 is formed with an inner cavity, the main portion of which is bounded by a circular transverse end face 200, a cylindrical face and a transverse annular face I38. The cylindrical head portion 65 of the pump rotor 65 divides this main portion into a pump balancing chamber I33 and an annular pump working chamber '16. Pump blade means 6! are mounted in axially extending recesses of the pump rotor, are slidable in axial direction, and slightlyproject with one end thereof into the pump balancing chamber I36 so as to be urged by the fluid pressure of a liquid contained therein against the cam means 69 as best seen from Figs. 10 and 11. For the sake of clarity, Fig. 11 shows only one pump blade 6'! but it will be understood that a plurality of pump blades is provided, as shown in Fig. 2.

The motor rotor 63 is provided with partitioning means 63 which project into the pump working chamber 56, dividing the same. Since the pump blades project through the working chamber it they cannot pass the partitioning means 68 and have to be pushed out of the working chamber 16 by the cam means 69, which are accordingly shaped. During rotation, the pump blades 6? form together with the partitioning means 68 a suction portion and a pressure portion in the pump working chamber 76, as can best be seen from Fig. 2.

The outer surface of the motor rotor 62 is formed with a transverse annular face 293, a cylindrical face 204 and a second transverse annular face its which define an annular cavity 2% together with the inner surface of the outer casing 6!. As can be best seen from Figs. 1 and 10, the stator means 13 is formed with an annular projection '13 projecting into the annular cavity 205 and dividing the same into an annular motor balancing chamber [3! and an annular motor working chamber H. Motorblade means M are mounted in axially extending recesses of the stator means it slightly projecting into the motor balancing chamber I31 so as to be urged by the fluid pressure of a liquid contained in the balancing chamber 13? against the cam means 12. During rotation of the motor rotor 62 the blades are retracted from the motor working chamber 1'? and pushed into the motor balancing chamber I31 by the cam 12 in order to permit passing of the partitioning means H which are secured to and rotate with the motor rotor 62. The cam means 72 and 69 are secured to the partitioning means H and 68, respectively, by means of screws 206 and consequently rotate with the rotor motor 62.

The cam faces of the cams G9 and 12 are of such a shape that during the relative rotation of rotor 62 with respect to rotor 65 and to the stator means 13, blades 6? and M bear continuously with their end faces against the associated annular faces I38 and 139 of rotor 62 so as to extend through the annular working chambers f6 and H, thus forming expansible working areas in these chambers.

The rotor motor is formed with conduits l9 and 18 connecting the pump working chamber 16 with the motor working chamber '11.

The operation of the combined pump and motor transmission is as follows:

When the drive shaft 66 is rotated, the pump rotor 65 and the blade means 6'! associated therewith rotate and push the liquid out of the pressure chamber portion of the pump working chamber 16 through conduit 19 into the receiving chamber portion of the motor working chamber l1, while the liquid is sucked from the discharge portion of the motor working chainber H through conduit 18 into the suction chamber portion of the pump working chamber 16, as indicated by arrows in Fig. 2. Thereby the motor rotor 52 is rotated and drives the driven shaft 53, the blades it being axially retracted by cam means 72 when located opposite partitions H.

The position of the axially movable drum 13, which constitutes the stator means, is defined by control means including a fluid valve means H4 mounted on the casing BI and formed with two spaced ports H5, H6 opening on a face which is slidably seated on a surface portionof the stator means 13. The ports I I5, and H6 co- One end of the conduit I I1 communicateswith the motor balancing chamber I31, while the other end is either located intermediate theconduits I I and I I6, asshown in'Fig. l, or communicates with one of .these ports :when the valve 1.1.4 is shifted. Fluid valve means II 4 is connected by pivoted connecting means H8 with another fluid valve means I.I9 cooperating withthe pump rotor -65. Pump rotor 65 is 'formed with a conduit 207 which corresponds to conduit I I1.in the stator means 13, and connects the pump balancing chamber 136 with the surface portion of pump rotor 65 on which the valve means 119 is seated. Valve means I19 is formed with two ports 208 and .209 which are connected to the pressure and suction portions, respectively, of the pump working chamber 16 by conduits 2H), 2H and 2I2.

It will be understood that pressure and suction portions are created in the working chambers I6 and 11, respectively, since the operating liquid in the pump is under pressure between a blade and the partitioning means in front of the blade, while suction is exerted in a suction chamber portion created behind .the moving blade. The conduits 298, 209 and theconduitsrI IB, I I8 communicate, respectively, with the suction and pressure chamber portions of the associated working chambers 16 and 1:1.

When the fluidvalve I I4 is shifted in axial direction, one of the conduits I I5 and I I6 registers with conduit Ill and communicates with the motor balancing chamber 131, increasing or decreasing the pressure therein, respectively so that the stator means I3 is moved in axial direction toward or away from the annular transverse face I39 of the motor rotor whereby the volume of the motor working chamber is decreased, or increased respectively.

The operation of the fluid valve means'I I9 is similar, the pump balancing chamber I35 being connected through conduit .20! to the pressure chamber portion, or to the suction chamber portion of the pump working chamber I6 in accordance with the position of the valve IIL9 and of the ports 208 and 209 in the same.

Connecting means II'8 connects the valve means H4 and H9 .in such manner that one of the working chambers is increased in volume when the other of the working chambers is decreased in volume.

While the annular pressure area of the stator means I3 in the motor balancing chamber is greater than the annular pressure area I39 in the motor working chamber 11, a movement of the stator means I3 to the left' can take place when the motor balancing chamber I3! is .connected to the suction portion of the motor working chamber 1.! since the fluid pressure as well, and not only the pressurelarea is decisive for the movement of the stator means 13. On the 'annular surface 139 a median pressure is exerted cular head plates of the casing 61.

I liB'ItO the suction portion of :the working chamber 11. When-the motor balancing chamber is connected to the pressure portion of the motor working chamber .11, the stator means will move to the right.

The valve means II9 operates similar to valve means H4, the connecting means H8 assuring a simultaneous and coordinated operation of the two valves in such manner that the pump working chamber 16 is increasedin volume when the motor working chamber 11 is decreased in volume and vice versa.

During normal operation, one end of conduit II! will be .located between the two ports of the conduit H5, H6, and one end of conduit 201 will be located between the ports Band 209, since a slight axial movement of the stator means 13 and of the rotor 65, respectively, will result in registering of the associated conduit Ill or 207, respectively with one of the .ports whereby a return movement of the members 13 and '65 ise'ffected. Consequently the stator means II1 will be maintained in an intermediate position unless the values I14, I I9 areoperated.

In the conduits 78 and i9, hydraulically operated fluid valve means Bil and BI are arranged which are movable in axial direction between several positions, and which are shown in Figs. 2, 7, 8 and 9. The corresponding ducts 1-8, 119 are arranged, respectively, on either side of the same partitioning means H and are connected by two channels $2, 83' provided within the rotor 62. Into each of the ducts l8, l9, two further conduits 84, .85 open which communicate through the circular grooves 86, 8'! in the casing GI with the hydraulic accumulatorBB and with the reservoir 89, respectively. The valves 86 and BI are arranged, respectively, in the bores 91, 98, extending parallel to the axis of the rotor 62 in the same, and communicating through smaller ports with circulargrooves 99, it in the cir- In each bore 91, 98 two springs I02 and I03 are arranged which act in opposite directions on the associated valve. Each valve BI], 8i comprises three portions I04, I05 and I06, corresponding, re-

spectively, to forward drive, to neutral, and to rearward drive, as will be explained in greater detail hereinafter. The portion I94 of the valve associated with duct 18, which supplies pressure fluid for forward drive, communicates through longitudinal channels I01 with the groove 99. The portion I04 of the other valve 8| in the duct I9 is connected through a :duct l01a with the groove I00. The grooves 99, Ital are interconnected by ducts I08 and N39 with the four-way cock H0 which on the other hand is connected with the accumulator 88 and with the reservoir 89 through connecting conduit means.

The operation of the valve means BI and B2 is as follows:

The spring I02 and I03 are arranged to hold the valve 80, 8| in a position of equilibrium, see Figs. 4 and 8, in which the portions W5 register with the ducts I8 and I9, respectively and dividethe same in the two portions which do not communicate, while the openings of the channels 82, 83 are all located in the duct portion communicating with the chamber It and thereby with the pump. Consequently the pump is by-passed which corresponds to the neutral position of the transmission. At the same time, the portion of the duct 19 opening into working chamber 11, communicates with the channel '84 which is connected to the reservoir 89 through the circular grooves 81 in the casing SI, while the corresponding portion of duct I8 communicates with conduit 85 and annular groove 86, and through the three-way cock I29 with the reservoir 89 or with the accumulator 88 according to the position of the operating cock I23. In the first position a free wheel operation of the transe mission is obtained and the liquid forced to flow by the rotation of rotor 62 passes freely through a closed circuit including chamber TI and the reservoir 89. In the second position, hydraulic braking is obtained and the pressure of the liquid contained in the accumulator 88 opposes the rotation of the rotor 62.

By operating suitable operating means, such as the four-way cock II9, the accumulator 88 is connected with the duct I98, and the conduit I99 with the reservoir 89 so that the pressure fluid is effective in groove 99 and the valves 89, 8| are actuated and compress the springs I93 so that the ports I94 register with the ducts 18, I9 and allow the fluid to pass freely through ducts I8, I9 as illustrated in Fig. 2. When pump rotor 65 is rotated by shaft 56 in the direction of the arrow I, the portions of the blades 6! projecting into the pump working chamber I6, and providing the effective surfaces of the blades, act on one side of the partition 68 on the operating fluid to force the same into the motor working chamber TI through the ducts 19, while on the other side of the partitioning means 88 the projecting portion of the blades create suction to draw the operating medium from motor working chamber I1 into pump working chamber It.

The fluid is then circulated through the ducts I8, I9 as shown by the arrows, and the rotor 82' is forced to rotate in the direction of shaft 59 as shown by arrows, which correspond to forward drive. When the slide valves 89, M are placed in the position illustrated in Fig. 7, admitting pressure fluid into the groove I99, the valves close by means of portions I96 the ducts I8, I9 at a point intermediate the connections of the latter with the channels 82, 83 whereby any direct communication between chamber I6 and 1'! through ducts I8 and 79 is cut off, but another connection is formed by the channels 82, 83 which are arranged in such manner that the liquid delivered by the pump from pump working chamber I6 into the closed duct I9 passes through the channel 82 into the closed part of duct I8 through which the liquid is guided out of chamber 11 in the valve position illustrated in Fig. 8. The liquid then enters chamber 'II through the duct I9 which previously served for admission of liquid from the pump. The liquid from chamber TI passes through the duct 19 and duct 83 into the part of duct I9 which communicates with the suction chamber portion of the pump into which it returns. Consequently the flow of liquid in the annular working chambers I9 and TI is reversed and this results in a reversal of direction of rotation of the rotor 92 and consequently in rearward drive of the transmission. The slide valves 9I, 82 are moved to the position illustrated in Fig. 7 by admitting pressure fluid into the groove I99 by moving the four-way cock IIII into a position in which the hydraulic accumulator 38 communicates with the duct I99 and the reservoir 99 communicates with the duct I98.

When the volume of the motor working chamber 11 is great, and the volume of the pump working chamber 16 is small, the secondary rotor 92 rotates at a low speed compared to'thespeed of the drive shaft 66 whereby maximum speed reduction is obtained. If the volume of pump working chamber I6 is reduced to zero by shifting the control valve II9 to cause the pump rotor 65 to move in axial direction, the pump and the motor are disconnected corresponding to a neutral position. Direct drive is obtained when the volume of the pump working chamber I6 is a maximum and the volume of the motor working chamber TI is a minimum as illustrated in Fig. 1 in which the stator means I3 has moved to the right of the figure, vwhile rotor 65 has moved to the left of the figure to its extreme position. In this position ducts I8 and I9 are closed by stator means I3 and direct drive is obtained. In the intermediate positions of the rotor 65 and of the stator means I3, intermediate speed reduction ratios are obtained. It will be apparent that the transmission ratio can be varied continuously between direct drive and minimum and maximum forward and rearward speeds by operating the valve means I I4 and I I9.

The hydraulic transmission may be operated in another manner as well. During the displacement of each slide valve 89 from its neutral position (Fig. 8) into its forward drive position (Fig. 2) or rear drive position (Fig. 7) the one or the other of the portions [0511 situated on both sides of its portion I95 registers with the corresponding duct I8 or I9 (Fig. 9). During this temporary intermediate position of slide valves 89, the direct communication between the chambers I9 and TI! through ducts I8 and I9 is cut off and another communication is established between the delivery side of the pump and the channel communicating with the cock I23, while the portion of duct I9 communicating with the suction side of the pump registers with duct 84 connected to the reservoir 89. If .thecock I23 is then operated so as to put the channel 85 into communication with the accumulator 88, the apparatus works as a starter, the fluid under pressure within the accumulator starting rotation of the pump and flowing thereupon into the reservoir 89, as indicated by the arrows in Fig. 9.

To start the engine, it suffices therefore to bring the cock I23 into the position indicated above, then to open the cock, I I9 so as to introduce fluid under pressure into groove 99 or I99, accordingto the desired direction of rotation. If the cock H9 is then shut, the slide valves 89 will tend to return to their relieved position, but on account of the narrow cross-section of the bores I9'I, I9Ia, they-will return very slowly so that the portions Ia willremain in communication with the ducts' I8, I9 for sufiicient time to ensure starting of the apparatus. Thereupon, the cock H9 may be operated again so as to bring the slide valves '89 intothe position for forward drive .(Fig. 2) or rearward drive (Fig. 7) and to maintain such position.

In the case of the application of this hydraulic transmission to an automobile, the cock I23 may be controlled by the brake pedal so that when the latter is not depressed, cock I23 is in the position in which the channel 85 communicates with the reservoir 89 whereas when the pedal is depressed, the cock I23 establishes communication of said channelv 85 with the accumulator 88. The braking efiect .is then increased by increasing the volume of the chamber II by a connection between the brake pedal and the control valve means II4,- 9..

In a similar manner, it is easy to provide with 9 this arrangement an automatic change speed gear depending solely" on the movement of the gas throttling means of the engine.

Of course, the present invention isby no means limited tothe details of the embodiments illustrated or described only by way of example. Thus in particular in the embodiment illustrated in Fig. and covering the control means for the transmission ratio, the two slide valves. I I4 and I I9 are still coupled through a rocking member I I8 but it is-this latter whichis directly engaged by the control device which is mechanical in the case considered and is constituted by a sliding rod I21 controlled by an arrangement including a threaded member 128"moving inside a stationary nut member I29.

In the modified embodimentillustrated in Fig. 6, the slide valves I3I and I32. which are asso ciatedfor operation by the pivoted member I33, are carried by the rotor 52. A common control slide valve I 34", carried by the casing 6i allows admission of the fluid under pressure through the port I35 which is in permanent connection with the delivery end of the pump into slide valve I 3| while the" slide valve I32 is simultaneously connected with the suction end. It should be noted that the port I35 registers with the. distribution channel of the slide valve IM only for a very short time during each revolution of the rotor which makes the operation of the slide valve I3I and I32 comparatively slow and gradual. Consequently, the variation in volume of the working chambers 16 and "IT which is produced by the longitudinal displacement of the primary rotor 65 and of the drum l3 will also be slow.

This transmission is also easily adaptable to automatic control of the transmission ratio through a regulator of any type in the case of an automatic control depending on fluid pressure. It is therefore sufficient to connect the output control valve member for (such as I Id in Fig. 1, I28 in Fig. 5, or I34 in Fig. 6) or the pivoted connecting member I I8 or I I8, to a pressure responsive member actuated by pressure fluid against the action of a suitably sized spring; any increase or reduction of the fluid pressure will result a variation in output and consequently a variation in the transmission ratio as desired.

For certain applications where it is desirable to obtain maximum simplicity, it is possible to omit the oil reservoir and the accumulator which serve only for braking and starting. In the absence of any accumulator and reservoir, it is pref erable to circulate the fluid through a radiator in order to avoid any excessive heating of theoperating fluid.

It is also possible to provide a direct positive drive as in the usual gear transmission through direct mechanical engagement between the pri mary and the secondary rotor.

Furthermore, by reversing the primary and the secondary transmission parts, I obtain a speed multiplying device.

It will be understood that the elements described above may also find a useful application in other types of hydraulic transmissions. The invention is not intended to be limited to the details shown, since various modifications may be made without departing from the spirit of the present invention.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a hydraulic transmission arrangement, in combination, a stationary casing; a driven shaft 1'0 rotatably'mounted' in said casing; a motor rotor fixedly secured to'said' driven shaft and rotatably mounted in said casing, said motor rotor being formed-with an inner cavity having a main portion open at one end and bounded by'a circular transverse end face, a cylindrical face; a transverse annular face facing said end face, said motor rotor having an outer surface portion including an annular transverse end face, a cylindrical face, a-se'cond transverse annular face facing said first annular end face and defining with the inner surface of said casing an annular cavity; a'drive shaft rotatably mounted in said casing; a pump rotor mounted on said drive shaft slidable' in axial direction and non-rotatable, said pump rotor having a stepped cylindrical outer surface fitting into said inner cavity of said motor'rotor and closing said main portion, said motor rotor having a cylindrical head portion located insaid' main portion between said end face and said annular face and definingv with the said pump rotor in said inner cavity a closed cylindrical pump balancingchamber and an annular pump working chamber; stator means non-rotatably and axially slidably mounted on the inner surface of said casing, and having an annular projecting portion dividing'said annular cavity into anannnlar motor balancingchamber and an annular motor working chamber; partitioning means secured to said motor rotor and projecting into said pump working chamber and into said motor Working chamber and dividing each of said working chambers; pump blade means and motor blade means mounted, respectively, on said pump rotor and on said stator means slidable in axial direction, said blade means projecting with one end thereof into the associated balancing chambers and into the associated working chambers and defining in the latter chambers together with said partitioning means suction portions and pressure portions; cam means secured to said partitioning means and engaging the other end of said blade means for pushing the same into the associated balancing chambers and out of said working chambers when said blade means pass said partitioning means during rotation of said rotor; conduit means in said motor rotor connecting said pressure portion of each working chamber with the suction portion of the other of said working chambers; first fluid valve means associated with said pump rotor and being movable between two positions and connecting in one of said positions said pump balancing chamber with the pressure portion of said pump working chamber and in the other position with the suction chamber of said pump working chamber; second fluid valve means associated with said stator means and being movable between two positions and connecting in one of said positions said motor balancing chamber with the pressure portion of said motor working chamber and in the other position with the suction portion of said motor Working chamber; connecting means connecting said first and second fluid valve means so that each of said fluid valve means moves to said one position thereof when the other of said fluid valve means moves to said other position thereof, whereby the fiuid pressure in said balancing chambers is adjusted causing axial movement of said pump rotor and of said stator means for adjusting the volumes of said annular working chambers; and means for adjusting the position of at least one of said fiuid valve means.

2. A. hydraulic transmission arrangement as claimed in claim 1, wherein at least said second fluid valve means has a'face slidably engaging a surface portion of said stator means and formed with two spaced ports communicating with the pressure portion and with the suction portion of said motor working chamber, and wherein said stator means is formed with a conduit connecting said motor balancing chamber with said surface portion of said stator means at a point intermediate said two ports for connecting each of said ports through said conduit with said motor balancing chamber.

3. A hydraulic transmission arrangement as claimed in claim 1 and including a hydraulic ac cumulator; a reservoir; hydraulically operated valve means arranged in said conduit means; connecting conduit means connecting said hydraulic accumulator and said reservoir, respectively, with said hydraulically operated valve means; operating means located in said connecting conduit means for controlling the direction of flow of an operating liquid through said connecting conduit means to said hydraulically operated valve means, said motor rotor being formed with a channel system controlled by said hydraulically operated valve means so that in one position of said hydraulically operated valve means the direction of rotation of said motor rotor is reversed, and in another position of said hydraulically operated valve means said suction portion and said pressure portion of said pump working chamber are connected by a portion of said channel system for by-passing said motor working chamber.

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